A fiber filler is typically added to a thermoset resin such as those used in sheet molding compounds (SMC) or bulk molding compounds (BMC) in order to provide a variety of adjustable properties for the resulting article. Fillers are routinely added to reduce article cost, modify viscosity of pre-cured loaded resins, control article shrinkage, control surface finish, density, flammability, electrical conductivity, chemical resistance, and strength of the resulting thermoset formulation. Particulate fillers typically account for amounts ranging from 0-80 total weight percent with typical particle filler sizes ranging from 0.1 to 50 microns. In addition to particulate fillers, fiber fillers are typically present in a thermoset resin formulation to provide enhanced strength to the resulting article relative to particulate filler. Fiber fillers have traditionally included glass, carbon, polyimides, polyesters (PE), polyamides, and natural fibers such as cotton, silk, and hemp.
There is a growing appreciation that thermoset materials containing high density particulate fillers are difficult to recycle and pose added health risks when ground to a powder. While considerable effort has been expended to produce high performance SMC and BMC materials containing natural fibers, such efforts have met with limited success owing to poor interfacial interaction between natural fibers and the surrounding cured hydrophobic thermoset matrices. While progress has been made in the area of plasma pretreatment of natural materials, these efforts are complicated and largely focused on fibrous natural materials.
Thus, there exists a need for thermoset resin formulations containing pre-treated natural origin cellulosic fillers, especially particulate fillers.